# Is it possible to set a sphere as a constraint for a bone?

I would like this bone to slide on the surface of the sphere. How can I do this in blender? I looked at all the constraints but I couldn’t find a solution.

You can use a shrinkwrap bone constraint.

However, even better than that is to use a limit distance constraint on surface mode (which describes a mathematical sphere, as opposed to a mesh pseudo-sphere made out of flat faces.)

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That’s pretty cool, I didn’t know the Shrinkwrap bone constraint.

Would there be a way for an object/bone/empty to stick on a NURBS surface and to input U and V values to control it’s position on the surface?

I tried the Shrinkwrap bone constraint but it can move erratically on an irregular surface.

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You can always do some C-C subdivision on a shrinkwrap target to smooth out the angles. It’ll never be perfect, but it can get good enough. For some reason, it really doesn’t seem to impact performance at all, not with a non-rendering shrinkwrap target, even though I’d expect it to. The subdivision doesn’t have to be re-evaluated to evaluate the shrinkwrap which helps.

Sorry, no way to define a nurbs surface for a bone’s position, although I agree, something like that would be cool. It would be nice to have more mathematical definitions for bone placement (because existing angle limit constraints are awful.)

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Not sure what you mean by C-C but the “Shade Smooth” makes the bone slide super smoothly along the surface, which is unexpected but nice!

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Catmull clark subdivision.

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Regretfully not. Projection is pretty much all you get with shrinkwrap. It would be lovely to have though! Shrinkwrap always felt like a poor man’s surface constraint to me.

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